Sendust alloys known as high permeability alloys consist of 6-12% of Si, 3-10% of Al with the remainder being substantially of Fe. Such alloys are very brittle in the cast state and readily become powder; therefore, plastic working is very difficult and the cutting and grinding of these alloys must be conducted very carefully which renders such operations highly expensive. Various Sendust multi-element alloys (abbreviated as Sendust series alloys hereinafter) in which various other elements are contained in order to improve the mechanical or magnetic properties of the above described Si-Al-Fe ternary Sendust alloys, have been known, and it has been disclosed in Japanese Patent Laid-Open Application No. 123,314/77 that Sendust series alloys containing a total amount of not more than 7.0% of at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Ni, Co, Cu, Ti, Mn, Ge, Zr, Sb, Sn, Be, B, Bi, Pb, Y, and rare earth elements are excellent in magnetic properties while having a high hardness and abrasion resistance, and therefore, these alloys are used for magnetic head cores of magnetic audio and video recordings.
According to the above described laid-open application, these Sendust series alloys have a high hardness but are very brittle. Therefore, forging and rolling are difficult, so the manufacture of a thin sheet-shaped core constructing the magnetic head relies upon mechanical cutting of a cast ingot. However, in the manufacturing process, fine cracks and notches are formed. Such cracks and notches lead to the great problem of poor yield for the product. A method for simply producing thin ribbon-shaped Sendust series alloys without causing such difficulties in mechanical working has been proposed. This method for producing Sendust series alloys is characterized in that a Sendust series molten alloy in a crucible is ejected onto the surface of a cooling substance moving in a constant direction at a rate of more than 1 m/sec from a nozzle to obtain a ribbon-shaped solidified Sendust series alloy, and the properties of ribbon-shaped Sendust series alloys consisting of 83.7% of Fe, 9.2% of Si, 5.6% of Al, and 1.5% of Y, as well as the properties of ribbon-shaped Sendust series alloys consisting of 84.0% of Fe, 9.0% of Si, 5.0% of Al, 1.0% of Al, 0.8% of Ti and 0.2% of Zr shown and there has been described with the effective permeability of these alloys in 100 KHz being 1,170 and 1,200 respectively.
The production method proposed in the above described laid-open application is one belonging to a category known as a usual method of quenching a molten metal wherein a molten metal is ejected onto a moving cooling surface of a cooling substance from a nozzle to quench and solidify the molten metal to obtain an amorphous or microcrystalline metal thin strip, and in this method, a Sendust series alloy is used as a molten metal.
The inventors have found that when a Sendust series alloy thin strip containing at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Ni, Co, Cu, Ti, Mn, Ge, Zr, Sb, Sn, Be, B, Bi, Pb, Y and rare earth elements in a total amount of not more than 7.0% disclosed in the above described laid-open application is formed by the quenching method, a major part of alloys have no satisfactory tensile strength and flexibility, and these thin strips cannot be worked and commercially used as a magnetic head, or as a core of a voltage or current transformer.
An object of the present invention is to provide a microcystalline thin strip for magnetic material having high permeability and high tensile strength as well as flexibility, in which the low tensile strength and flexibility possessed by already known microcrystalline thin strips are improved. Another object of this invention is to provide a method for producing the same thin strip and articles made from the thin strip.